1. Field of the Invention
The present invention concerns an optoelectronic device on an semi-insulator substrate as well as various methods for making such a device.
2. Description of the Prior Art
At present, there is a growing interest in the transmission, by optical fibers, of very high frequency signals such as "radar" signals. Thus, it can be seen that there is a great demand for the development of optoelectronic devices by which the X band (8-12 GHz) or K.sub.U band (12-18 GHz) can be attained. At present, buried strip type lasers can be used to attain 10 GHz. Such lasers are constituted, for example, by a strip of active material provided between two confinement layers, namely a lower layer and an upper layer, each layer having a different type of conductivity, this entire unit being made on a semiconductor substrate. In fact, the limitation of these strips in frequency arises essentially out of the stray elements located on either side of the active strip, especially from the stray capacitances due to the P-N homojunction formed by the overlapping of the two confinement layers located on either side of the active strip.
The present invention is therefore aimed at achieving a notable reduction in this capacitance by proposing a new structure of an optoelectronic device made on a semi-insulator substrate.